The inner shell of the freezer is probably also aluminum. This could work with a polyethylene liner inside of it. A closed loop system with a small gas hot water (if you're on residential gas) and a 3/4 inch black steel pipe grid heat exchanger in the tank with a small electric pump pulling heating fluid into the cold inlet could provide enough heat for that. Use 50/50 antifreeze (corrosion protection) in the loop and install a vented tank recovery tank to the high temperature/high pressure relief valve. Mount the heat exchanger vertically in the back of the unit, hot water in on the bottom and cold on top.
